Dry electrode manufacture by temperature activation method

ABSTRACT

A method of manufacturing a free-standing electrode film includes preparing a mixture including an electrode active material, a conductive material, and a binder, heating the mixture to 70° C. or higher, subjecting the mixture to a shear force, and, after the mixture has been subjected to the shear force, pressing the mixture into a free-standing film. The method may further include adding a solvent to the mixture. A resulting free-standing electrode film may include an amount of binder less than 4% by weight.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application relates to and claims the benefit of U.S. Provisional Application No. 62/857,144, filed Jun. 4, 2019 and entitled “DRY ELECTRODE MANUFACTURE BY TEMPERATURE ACTIVATION METHOD,” the entire disclosure of which is hereby incorporated by reference.

STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT

Not Applicable

BACKGROUND 1. Technical Field

The present disclosure relates generally to manufacturing electrodes for energy storage devices such as batteries and, more particularly, to the manufacture of a free-standing electrode film by a dry process.

2. Related Art

As demand for inexpensive energy storage devices increases, various methods have been proposed for manufacturing electrodes. Among these, there exist so-called “dry” processes by which a free-standing electrode film may be manufactured while avoiding the expense and drying time associated with the solvents and aqueous solutions that are typically used in slurry coating and extrusion processes. In order to produce higher quality electrodes by such a dry process that may result in energy storage devices having higher energy density, the amount of binder mixed with the active material should be minimized within a range that still allows for an electrode film to be reliably produced without excessive breakage. To this end, the binder may be activated to improve its adhesion strength by the addition of a highly vaporizable solvent as described in the present inventor's own U.S. Pat. No. 10,069,131, entitled “Electrode for Energy Storage Devices and Method of Making Same,” the entirety of the disclosure of which is wholly incorporated by reference herein. However, further reduction in the amount of binder needed is desirable, especially in the case of producing electrodes for batteries, where maximizing the active material loading is essential to maximizing the energy density of the battery.

BRIEF SUMMARY

The present disclosure contemplates various methods for overcoming the drawbacks accompanying the related art. One aspect of the embodiments of the present disclosure is a method of manufacturing a free-standing electrode film. The method may include preparing a mixture including an electrode active material, a conductive material, and a binder, heating the mixture to 70° C. or higher, after said heating, subjecting the mixture to a shear force, and, after the mixture has been subjected to the shear force, pressing the mixture into a free-standing film.

The method may further include adding a solvent to the mixture before the mixture is subjected to the shear force. Adding the solvent to the mixture may be performed after the heating.

The method may further include adding a solvent to the mixture while the mixture is being subjected to the shear force.

Subjecting the mixture to the shear force may include mixing the mixture in a high shear mixer, such as a kitchen or industrial blender (e.g. a Waring® blender), a cyclomixer, a jet mill, a bead mill, a planetary mixer, a paddle mixer, etc.

The pressing may include applying a roller press to the mixture.

The solvent may have a boiling point of less than 130° C. or less than 100° C. The solvent may include one or more chemicals selected from the group consisting of: a hydrocarbon, an acetate ester, an alcohol, a glycol, ethanol, methanol, isopropanol, acetone, diethyl carbonate, and dimethyl carbonate.

Another aspect of the embodiments of the present disclosure is a method of manufacturing a free-standing electrode film. The method may include preparing a mixture including an electrode active material, a conductive material, and a binder, adding a solvent to the mixture, after the solvent has been added to the mixture, subjecting the mixture to a shear force, after the mixture has been subjected to the shear force, heating the mixture to 70° C. or higher, and, after heating, pressing the mixture into a free-standing film.

Subjecting the mixture to a shear force may include mixing the mixture in a high shear mixer, such as a kitchen or industrial blender (e.g. a Waring® blender), a cyclomixer, a jet mill, a bead mill, a planetary mixer, a paddle mixer, etc.

The pressing may include applying a roller press to the mixture.

The solvent may have a boiling point of less than 130° C. or less than 100° C. The solvent may include one or more chemicals selected from the group consisting of: a hydrocarbon, an acetate ester, an alcohol, a glycol, ethanol, methanol, isopropanol, acetone, diethyl carbonate, and dimethyl carbonate.

Another aspect of the embodiments of the present disclosure is a method of manufacturing an electrode. The method may include performing any of the above methods of manufacturing a free-standing electrode film and laminating the resulting free-standing film on a current collector.

Another aspect of the embodiments of the present disclosure is a free-standing electrode film including an electrode active material, a conductive material, and one or more binders, the one or more binders totaling around 4% by weight of the free-standing electrode film, and in some cases less than 4%.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

The above and other features and advantages of the various embodiments disclosed herein will be better understood with respect to the following description and drawings, in which like numbers refer to like parts throughout, and in which:

FIG. 1 shows an operational flow for manufacturing a free-standing electrode film or an electrode produced therefrom;

FIG. 2 shows a free-standing electrode film produced by a process having no activation step;

FIG. 3 shows a free-standing electrode film produced by a single activation process having only a solvent activation step; and

FIG. 4 shows a free-standing electrode film produced by a dual activation process having both a solvent activation step and a temperature activation step.

DETAILED DESCRIPTION

The present disclosure encompasses various embodiments of methods for manufacturing a free-standing electrode film or an electrode produced therefrom. The detailed description set forth below in connection with the appended drawings is intended as a description of several currently contemplated embodiments, and is not intended to represent the only form in which the disclosed invention may be developed or utilized. The description sets forth the functions and features in connection with the illustrated embodiments. It is to be understood, however, that the same or equivalent functions may be accomplished by different embodiments that are also intended to be encompassed within the scope of the present disclosure. It is further understood that the use of relational terms such as first and second and the like are used solely to distinguish one from another entity without necessarily requiring or implying any actual such relationship or order between such entities.

FIG. 1 shows an operational flow for manufacturing a free-standing electrode film or an electrode produced therefrom. Unlike conventional dry processes, the process exemplified by FIG. 1 may include a temperature activation step that may be performed instead of or in addition to the solvent activation contemplated by U.S. Pat. No. 10,069,131. In the temperature activation step, the temperature of the binder used to form the free-standing electrode film may be raised, causing the binder to become softer and able to stretch longer and finer before breaking. As a result, the amount of binder needed to reliably produce a free-standing electrode film may be reduced.

The operational flow of FIG. 1 may begin with a step 110 of preparing a mixture (e.g. a powder mixture) including an electrode active material, a conductive material, and a binder. Depending on the energy storage device to be produced, the electrode active material may be, for example, activated carbon, graphite, hard carbon, or a metal oxide such as manganese dioxide, with the conductive material comprising metal particles or conductive carbon such as activated carbon, graphite, hard carbon, or carbon black. In the case of manufacturing an electrode for use in a battery, the electrode active material may be, for example, lithium manganese oxide (LMO) in an amount 82-99 percent (e.g. 93%) by weight of the mixture and the conductive material may be, for example, activated carbon in an amount 0-10 percent (e.g. 3.5%) by weight of the mixture. The binder may, for example, be polytetrafluoroethylene (PTFE) or another thermoplastic polymer and may be in an amount 1-8 percent by weight of the mixture, preferably equal to or less than 4 percent, more preferably less than 4% (e.g. 3.5%).

The operational flow of FIG. 1 may continue with a temperature activation step 120 of heating the mixture to 70° C. or higher, preferably 100° C. or higher, and, in some cases, a solvent activation step 130 of adding a solvent to the mixture. In the temperature activation step 120, the temperature to which the mixture is heated may be less than the glass transition temperature of the binder (e.g. 114.85° C. for PTFE), as softening of the binder may occur prior to reaching the glass temperature. Alternatively, the mixture may be heated to a temperature equal to or greater than the glass temperature of the binder. The solvent activation step 130, if performed, may cause the binder to soften further and become more able to stretch without breaking. Unlike solvents such as N-Methyl-2-pyrrolidone (NMP) that may be difficult to remove and entail lengthy drying processes, the solvent added in the solvent activation step 130 may have a relatively low boiling point of less than 130° C. or less than 100° C. (i.e. less than the boiling point of water). The solvent may include one or more chemicals selected from the group consisting of a hydrocarbon, an acetate ester, an alcohol, a glycol, ethanol, methanol, isopropanol, acetone, diethyl carbonate, and dimethyl carbonate. Unlike slurry coating and extrusion processes in which the solvent may be 60-80% by weight of the resulting wet mixture, the present disclosed process may add a relatively small amount of solvent in step 130, amounting to less than 20% of the resulting mixture. For example, the ratio of the powder mixture to the added solvent may be around 100:3.

With the binder having been activated by one or both of the activation steps 120, 130, the operational flow of FIG. 1 may continue with a step 140 of subjecting the mixture to a shear force. The mixture may, for example, be blended in a blender, such as an ordinary kitchen blender or an industrial blender. Adequate shear force to deform (e.g. elongate) the binder, resulting in a stickier, more pliable mixture, may be achieved by blending the mixture in such a blender at around 10,000 RPM for 1-10 min (e.g. 5 min). As another example, instead of being blended in a blender, the mixture may be ground in a jet mill.

After the mixture has been subjected to the shear force, the operational flow of FIG. 1 may continue with a step 150 of pressing the mixture to produce a free-standing film, for example, using a roller press. The resulting free-standing film, which may have an amount of binder less than 4% by weight of the free-standing electrode film, may thereafter be laminated on a current collector (e.g. copper or aluminum) to produce an electrode in a step 160.

As noted above, the solvent activation step 130 may be completely omitted, with the binder still being adequately activated by the temperature activation step 120. In such case, step 140 of subjecting the mixture to a shear force (e.g. using a blender of jet mill) may follow the temperature activation step 120. In the case of a “dual activation” process including both the temperature activation step 120 and the solvent activation step 130, the shear force of step 140 may be applied after the binder has been activated by one or both of the activation steps 120, 130 as noted above. For example, steps 120, 130, and 140 may be performed one after the other in the order shown in FIG. 1 . Alternatively, the solvent activation step 130 may be combined with step 140 such that, for example, the solvent may be injected into the mixture while the mixture is being subjected to the shear force. As another possibility, steps 130 and 140, whether subsequently performed or combined, may precede the temperature activation step 120, such that the two activation steps 120, 130 occur respectively before and after the mixture is subjected to the shear force in step 140.

FIG. 2 shows a free-standing electrode film produced by a process having no activation step. In accordance with step 110 of FIG. 1 , a mixture was prepared including 93% lithium manganese oxide (LMO) as an electrode active material, 3.5% activated carbon as a conductive material, and polytetrafluoroethylene (PTFE) as a binder. In accordance with step 140, the mixture was subjected to a shear force by being blended in a Waring® blender for five minutes. Then, in accordance with step 150, the mixture was pressed by a roller press at a temperature of 150° C. and a roll gap of 20 μm. As can be seen in FIG. 1 , the resulting film fell apart into a few pieces. The film was relatively thick at around 400 μm, which would make it difficult to achieve a typical final electrode thickness of less than 200 μm.

FIG. 3 shows a free-standing electrode film produced by a single activation process having only a solvent activation step. Again, in accordance with step 110 of FIG. 1 , a mixture was prepared including 93% lithium manganese oxide (LMO) as an electrode active material, 3.5% activated carbon as a conductive material, and polytetrafluoroethylene (PTFE) as a binder. This time, however, acetone was added in a solvent activation step 130 at a powder mixture to acetone ratio of 100:3. In accordance with step 140, the mixture was then subjected to a shear force by being blended in a Waring® blender for five minutes. Then, in accordance with step 150, the mixture was pressed by a roller press at a temperature of 150° C. and a roll gap of 20 μm. As can be seen in FIG. 3 , the resulting film remained mostly in one piece, but with a large slit in the middle. Owing to being more flexible and less brittle than the film of FIG. 2 , the film was somewhat thinner at around 380 μm.

FIG. 4 shows a free-standing electrode film produced by a dual activation process having both a solvent activation step and a temperature activation step. Again, in accordance with step 110 of FIG. 1 , a mixture was prepared including 93% lithium manganese oxide (LMO) as an electrode active material, 3.5% activated carbon as a conductive material, and polytetrafluoroethylene (PTFE) as a binder. Also, as in the example of FIG. 3 , acetone was added in a solvent activation step 130 at a powder mixture to acetone ratio of 100:3. In accordance with step 140, the mixture was then subjected to a shear force by being blended in a Waring® blender for five minutes. In accordance with step 150, the mixture was similarly pressed by a roller press at a temperature of 150° C. and a roll gap of 20 μm. This time, however, prior to pressing the mixture, the mixture was set on the roller press and preheated at 150° C. for 10 minutes in a temperature activation step 120, during which the temperature of the mixture reached 70° C. or higher. As can be seen in FIG. 4 , the resulting film remained in one piece. Also, owing to being more flexible and less brittle than the film of FIG. 3 , the film was even thinner at around 360 μm.

The experimental results described in relation to FIG. 2-4 are summarized in the following table.

TABLE 1 Comparative Example 1 Comparative Example 2 Embodiment Example (FIG. 2) (FIG. 3) (FIG. 4) Powder 93% LMO, 93% LMO, 93% LMO, Composition 3.5% activated carbon, 3.5% activated carbon, 3.5% activated carbon, 3.5% PTFE 3.5% PTFE 3.5% PTFE Binder Activation No activation Solvent activation: Dual activation: powder to powder to acetone ratio of acetone ratio 100:3 of 100:3 preheated at 150° C. for 10 minutes prior to pressing Shear Force Blended in Waring ® Blended in Waring ® Blended in Waring ® blender for 5 minutes blender for 5 minutes blender for 5 minutes Pressing Pressed by roller press Pressed by roller press Pressed by roller press Condition at 150° C. at roll gap of at 150° C. at roll gap of at 150° C. at roll gap of 20 μm 20 μm 20 μm Film Quality Film fell apart into a Film almost in one Film in one piece, few pieces piece but with large more flexible and less slit in the middle, brittle than Comp. more flexible and less Example 2 brittle than Comp. Example 1 Film Thickness 400 μm 380 μm 360 μm

As can be understood from the above Table 1 and FIGS. 2-4 , for a given quantity of binder (e.g. 3.5% PTFE), the addition of a temperature activation step 120 may result in a free-standing electrode film having superior quality and thickness relative to a dry method having only a solvent activation step 130. As such, the disclosed methods can be understood to reduce the quantity of binder needed to produce a free-standing electrode film of acceptable quality.

According to the disclosed methods, a free-standing electrode film can be produced comprising an electrode active material, a conductive material, and one or more binders totaling less than 4% by weight of the free-standing electrode film. Such a free-standing electrode film with reduced quantity of binder can be laminated to a current collector to produce an electrode for use in batteries, ultracapacitors, lithium ion capacitors (LIC), fuel cells, and other energy storage devices having higher energy density and lower manufacturing costs.

The above description is given by way of example, and not limitation. Given the above disclosure, one skilled in the art could devise variations that are within the scope and spirit of the invention disclosed herein. Further, the various features of the embodiments disclosed herein can be used alone, or in varying combinations with each other and are not intended to be limited to the specific combination described herein. Thus, the scope of the claims is not to be limited by the illustrated embodiments. 

1-20. (canceled)
 21. A free-standing electrode film comprising: an electrode active material; and one or more binders totaling less than 4 percent by weight of the free-standing electrode film, the electrode active material having an exposed surface that is unblocked by the one or more binders.
 22. The free-standing electrode film of claim 21, wherein the one or more binders comprise polytetrafluoroethylene (PTFE).
 23. The free-standing electrode film of claim 21, wherein the one or more binders total 3.5 percent by weight of the free-standing electrode film.
 24. The free-standing electrode film of claim 21, wherein the electrode active material is in an amount 82-99 percent by weight of the free-standing electrode film.
 25. The free-standing electrode film of claim 21, wherein the electrode active material comprises one or more materials selected from the group consisting of activated carbon, graphite, hard carbon, and metal oxide.
 26. The free-standing electrode film of claim 21, further comprising a conductive material.
 27. The free-standing electrode film of claim 26, wherein the conductive material is in an amount less than 10 percent by weight of the free-standing electrode film.
 28. The free-standing electrode film of claim 27, wherein the conductive material is 3.5 percent by weight of the free-standing electrode film.
 29. The free-standing electrode film of claim 21, further comprising solvent in an amount less than 3 percent by weight of the free-standing electrode film.
 30. The free-standing electrode film of claim 29, wherein the solvent has a boiling point of less than 130° C.
 31. The free-standing electrode film of claim 29, wherein the solvent includes one or more chemicals selected from the group consisting of a hydrocarbon, an acetate ester, an alcohol, a glycol, ethanol, methanol, isopropanol, acetone, diethyl carbonate, and dimethyl carbonate.
 32. An electrode for use in an energy storage device, the electrode comprising: a current collector; and an electrode film laminated on the current collector, the electrode film comprising an electrode active material and one or more binders totaling less than 4 percent by weight of the electrode film, the electrode active material having an exposed surface that is unblocked by the one or more binders.
 33. The electrode of claim 32, wherein the one or more binders comprise polytetrafluoroethylene (PTFE).
 34. The electrode of claim 32, wherein the one or more binders total 3.5 percent by weight of the electrode film.
 35. The electrode of claim 32, wherein the electrode active material is in an amount 82-99 percent by weight of the electrode film.
 36. The electrode of claim 32, wherein the electrode active material comprises one or more materials selected from the group consisting of activated carbon, graphite, hard carbon, and metal oxide.
 37. The electrode of claim 32, wherein the electrode film further comprises a conductive material.
 38. The electrode of claim 37, wherein the conductive material is in an amount less than 10 percent by weight of the electrode film.
 39. The electrode of claim 38, wherein the conductive material is 3.5 percent by weight of the electrode film.
 40. The electrode of claim 32, wherein the electrode film further comprises solvent in an amount less than 3 percent by weight of the electrode film. 